The present invention relates to an air duct for use in air conditioning facilities in buildings and to a paper for use in the air duct, and in particular an air duct in which condensation thereon is prevented from dripping as well as to a paper to be wound around a tubular member to insulate the air duct.
Air ducts composed of a tubular member of a square, oblong, or circular cross-section made of a tin or aluminum sections are indispensable as conduits materials for air conditioning facilities in buildings. Among various ducts of these kinds, a rectangular duct, a round duct, a spiral duct, and a flexible spiral duct are well-known.
As illustrated in FIG. 1, the rectangular duct is constructed by shaping metal sheets into tubular members 1 of a square or oblong cross-section and connecting the tubular members 1 together in a longitudinal direction by means of S-shaped seams 2. The round duct is formed by curving metal sheets into tubular members of a circular cross-section and connecting the tubular members in a longitudinal direction by means of grooved seams. The spiral duct is constructed by winding metal sheets spirally into tubular members of a circular cross-section and connecting the ends of the metal sheets by means of grooved seams.
Furthermore, the flexible spiral duct is formed by winding metal sheets of uniform width spirally into a tubular member, and as shown in FIGS. 2 and 3, corrugated ribs are formed on the surface thereof mainly in order to enhance the strength and workability of the tubular member. The flexible spiral duct of FIGS. 2 and 3 is disclosed in Japanese Utility Model Application, B-Publication (Koukoku) No. 3-17105, and comprises a tubular member 10 formed by winding a metal sheet of a prescribed width spirally while seaming the lateral ends thereof. Several corrugated ribs 12 are formed between the adjacent two seams 11 and 11 of the tubular member, whereby the flexible spiral duct is expansible and contractible in an axial direction thereof. During the construction of an air duct facility, the flexible duct in a contracted state is simply expanded to a desired length, bent as necessary, and secured. Thus, the use of the flexible duct enables bent arrangements for the piping and allows easier piping installation. For manufacturing the flexible spiral duct as described above, as shown, for example, in FIG. 4, a metal sheet 13 is fed into a shaping machine 14 to form the corrugated ribs 12 along the moving direction, and is then wound spirally on a roll 15 arranged obliquely with respect to the above moving direction. Subsequently, the lateral ends of the metal sheet are seamed to provide a continuous tubular member 10.
When the air ducts as described above are used in pipings for air conditioning facilities in buildings such as pipes for cooling or intake pipes for ventilation, cooled air is caused to flow through the air ducts, and water vapor contained in the ambient air is condensed on the outer peripheral surface of the ducts due to the temperature difference between the inside and outside of the duct.
This condensation may cause the air duct to corrode, thereby reducing the service life thereof. Furthermore, the condensation droplets may stain the ceiling, the walls, the floor and so on, or may otherwise reduce the service life of the buildings. The condensation on electrical wiring may cause short circuiting.
Conventionally, for the prevention of the condensation, heat insulating material such as rock wool, glass fiber, urethane foam resin, nonwoven fabric, or the like is wound on the outer periphery of the air duct, and is fixedly secured thereto by covering the entire duct with a tape or a metal sheet.
However, the above conventional method of using heat insulating materials requires laborious work inside the insulating material must be wound at the construction site after the air duct is installed. Therefore, increased expenses cannot be avoided. In addition, the work space is often very small and even dangerous in some cases. In particular, in the case where a flexible spiral duct is employed as the air duct, the advantages of using this type of duct will be lost.
Moreover, even though heat insulating materials are employed, it is very difficult to completely prevent condensation. Therefore, when cooled air is allowed to run through the duct, condensation, even if slight, inevitably condenses on the outer periphery of the duct and is absorbed into the insulating material. However, heat insulating material generally is poor in releasing water, and its outer periphery must be almost entirely covered with a tape or a metal sheet. Consequently, even after the supply of cooled air into the duct ceases, the water absorbed into the heat insulating material remains therein and does not evaporate. This causes the duct to corrode. Furthermore, since the condensation which penetrated into the heat insulating material gradually accumulates therein, the heat insulating efficiency is thereby lowered. The droplets from the heat insulating material may further stain the ceiling, the walls, the floor and so on, or may otherwise reduce the service life of the buildings. Condensation on the electrical wiring may cause short circuiting.
Moreover, when the heat insulating material is wound around the aforesaid flexible spiral duct, gaps inevitably form between the heat insulating material and the corrugated ribs formed on the tubular member, and water absorbed into the heat insulating material may remain in the gaps and thereby accelerate the corrosion of the duct.
Furthermore, since the heat insulating material contains a high proportion of resin constituents, it burns easily, and additionally, during a fire, toxic gases are produced.